Stereoscopic photography

ABSTRACT

Stereoscopic photographs, exhibiting the effect of parallax about both horizontal and vertical axes, are recorded on a lenticular film or a lenticular screen-film combination located at the focus of the camera objective, the lenticules on the film or screen having substantially spherical curvature and peripheries with a space-filling configuration, such as square or hexagonal, so oriented that there are no appreciable nonlenticulated areas between adjacent lenticules. Said configuration matches, to a reduced scale, that of an aperture in a plate or diaphragm located in the plane of one of the lens pupils. The characteristics of the lens, the aperture and the lenticles are so coordinated that the elementary image formed at the focus of each lenticule substantially fills the format of that lenticule so that adjacent elementary images are neither appreciable spaced apart nor overlapping. The completed photograph, or a reproduction thereof, exhibits a stereoscopic effect when viewed through the lenticulated surface or through another screen which matches that used in taking the picture. Also disclosed are methods and apparatus for manufacturing such lenticular film and screens, methods of copying the photographs, methods of recording and viewing stereoscopic color photographs on black-and-white stock, and the adaptation of the system to aerial photography and to television.

STEREOSCOPIC PHOTOGRAPHY [72] Inventor: Leslie Peter Dudley, Los Angeles,

Calif.

[73] Assignee: Dudley Optical Laboratories, Inc.,

Beverly Hills, Calif. [22] Filed: July 26, 1968 [21] App]. No.: 747,931

[52] US. Cl. ..95/18 [51] Int. Cl. ..G03b 35/08 [58] Field of Search ..95/18 [56] References Cited UNITED STATES PATENTS 3,387,547 6/1968 Houghton ..95/36 2,622,472 12/ 1952 Bonnet ..95/ 18 P X 2,950,644 8/ 1960 Land ..95/18 P X 3,291,555 12/1966 Browning ..95/18 P X 1,905,716 4/1933 lves ..95/18 P 1,918,705 7/1933 Ives ..95/l8 P 1,935,471 ll/l933 Kanolt ..95/18 P 2,063,985 12/1936 Coffey ..95/18 P 2,724,312 11/1955 Gruetzner ..95/18 P [is] 3,683,773 [451 Aug. 15, 1972 ABSTRACT Stereoscopic photographs, exhibiting the effect of parallax about both horizontal and vertical axes, are recorded on a lenticular film or a lenticular screenfilm combination located at the focus of the camera objective, the lenticules on the film or screen having substantially spherical curvature and peripheries with a space-filling configuration, such as square or hexagonal, so oriented that there are no appreciable nonlenticulated areas between adjacent lenticules. Said configuration matches, to a reduced scale, that of an aperture in a plate or diaphragm located in the plane of one of the lens pupils. The characteristics of the lens, the aperture and the lenticles are so coordinated that the elementary image formed at the focus of each lenticule substantially fills the format of that lenticule so that adjacent elementary images are neither appreciable spaced apart nor overlapping. The completed photograph, or a reproduction thereof, exhibits a stereoscopic effect when viewed through the lenticulated surface or through another screen which matches that used in taking the picture. Also disclosed are methods and apparatus for manufacturing such lenticular film and screens, methods of copying the photographs, methods of recording and viewing stereoscopic color photographs on black-and-white stock, and the adaptation of the system to aerial photography and to television.

13 Claims, 42 Drawing Figures PATENTEDAUG 15 we saw 020F 1 m E\ TOR 4654/6 P6766 DUDAEV A 7702M? V5 PATENTEDMIB 15 1972 3.683, 773

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BY 5M? A TEZA/E E STEREOSCOPIC PHOTOGRAPHY The present invention is concerned with an improved system of stereoscopic or three-dimensional photography. A photograph produced in accordance with one or another of the methods described in this specification exhibits optical characteristics closely resembling those of a hologram. Thus, the aspect of the recorded three-dimensional image changes with change of viewpoint about both horizontal and vertical axes. However, the new type of photograph, which may be appropriately termed an integram or integraph, possesses several important advantages over the hologram. For example, coherent light (e. g., laser illumination) is not required in either taking or viewing the picture. Further advantages are: The photographic equipment employed is compact and simple to operate; exposure timescorrespond to those which would be required for ordinary two-dimensional photography under the same conditions; action shots and/or the use of flash present no more difiiculty than with ordinary photography, and it is virtually impossible to produce an out-of-focus picture.

The photographic record constituting an integram consists of a large number of minute, juxtaposed images produced by an optical screen or reseau. The sameor a similar-screen is used when viewing the picture. In the preferred form, the screen consists of transparent material embossed on one surface with an array of small lenticules or lenslets of spherical or substantially spherical curvature. The screen is so located with respect to the photographic film emulsion or other photo-recording medium that the photo-recording surface is at the focus of the lenticules. A convenient arrangement is for the screen-film combination to be manufactured as a composite unit, the lenticules being embossed on the exterior surface of the film base.

In some applications of the present invention it is possible to employ, instead of a screen embossed with spherical lenticules, a device which may be regarded as the optical equivalent of such a screen. One type of optically equivalent screen is made from a pair of cylindrically lenticulated screens, the lenticulated surfaces of the two screens being in contact with each other, and the longitudinal axes of the lenticules of one screen being at right-angles to the longitudinal axes of the lenticules of the other screen. Another type of optically equivalent screen consists, in effect, of a sheet of opaque material pierced with a multiplicity of small apertures disposed in a regular array. In this case the apertures are not circular, like a pinhole, but are so shaped that adjacent images in the corresponding array of images are not appreciable overlapping or spaced apart; thus, apertures of square shape are very suitable. A satisfactory square-aperture screen can be produced by crossing two line screens which have an appropriate opaque/transparent ratio; then, by correct adjustment of the distance between the array of apertures and the sensitive surface, matters can be so arranged that adjacent images in the array are not overlapping or spaced apart by an excessive amount. There are, basically, two alternative techniques either one or the other of which may be used for production of an integram; one of these techniques is termed direct integraphy, and the other is referred to as indirect integraphy. The present application is concerned with the indirect method, the direct method being described in my co-pending U. S. patent application filed of even date herewith, Ser. No. 747,996.

In the indirect method of this invention, the screenfilm combination is used to record an integram of the aerial image of the scene or subject formed by a primary lens (e. g., camera objective). Thus, the screen-film combination can be located at the focal plane of a regular camera to which some slight modifications have been made; each lenticule then functions as a minute field lens, reimaging that portion of the image formed by the primary lens which would otherwise reach the film direct. In this indirect method, the degree of parallax is governed by the diameter of the primary lens. No focus adjustment is required for the purpose of ensuring sharpness, regardless of the distance of the subject, although the distance of the primary lens from the screen-film combination can be varied if desired. However, such adjustment has no effect on the sharpness of the imagery, but determines which particular transverse plane of the subject will appear to coincide with the film plane of the completed integram. The reimaging (by the lenticular array) process results in a tremendous increase in the depth of field that would otherwise be provided by the primary lens alone. The exposure can be varied by the use of a filter or filters and/or by adjustment of the shutter speed. The use of a primary lens of relatively large diameter is desirable, and a number of suitable (camera) lenses are currently available on the market. A significant consideration, moreover, is that lenses designed especially for indirect integraphy can be produced at costs substantially below those of equivalent lenses designed for regular photography. This is because the reimaging process renders it unnecessary to incorporate such precise correction for all the aberrations in the primary lens.

An important feature of the indirect method resides in the relationship which must exist between the characteristics of the primary lens, the characteristics of the lenticules, and the dimensions of a special type of aperture plate which is used in conjunction with the primary lens, no iris diaphragm being employed. The reason for this relationship is that it is necessary to ensure that adjacent images in the integraphic array are precisely abutting, and not appreciably overlapping or spaced apart.

It is preferred that the aperture plate consist of a mask of opaque material, the center portion of which is pierced to provide a clear aperture, square or hexagonal in shape, depending upon the characteristics of the lenticular array. In general, the f-number of the primary lens must be numerically lower than that of the lenticules. Then, by appropriate selection of the size of the aperture, the condition specified in the preceding paragraph can be fulfilled.

If desired, the camera can be provided with an adjustable aperture plate so that, either manually or automatically, the size of the opening can be varied according to the distance of the plane on which the camera is focused.

lntegrams produced by the indirect method present a predominance of stereoscopic zones when viewed from a comparatively short distance, such as that customarily adopted in normal reading. At greater viewing distances, pseudoscopic zones predominate. This state of affairs can be reversed, if desired, by adopting a suitable printing technique when making the positive; the picture will then appear predominantly pseudoscopic when viewed from a short distance, and predominantly stereoscopic when viewed from a greater distance.

It is sometimes desirable to be able to increase the horizontal parallax (stereoscopic base) to a degree beyond that equivalent to the diameter of the camera lens. Such occasions arise when, for example, it is necessary to photograph a distant landscape in which there are no objects in the immediate foreground, or when aerial photography is involved. To meet occasions in the former category, a special lightweight, mechanically operated, traversing-type camera-mounting can be employed. Exposure is made via a horizontally operating, focal-plane shutter while the camera shifts laterally through a predetermined distance. The stereoscopic base can be increased by this means by an amount equal to several times the interocular separation. The three-dimensional effect exhibited bythe resulting integram will be either predominantly stereoscopic or predominantly pseudoscopic depending upon whether the photo-recording device and the shutter slit are caused to move in opposite directions or the same direction. A miniaturized version of the camera-mounting described in my U. S. Pat. No. 2,572,994 (corresponding to British Pat. No. 656,165) could be adapted to the present purpose, but a less complex device may be employed, if desired.

In the case of aerial photography, the special mounting referred to above is not required, the increase in stereoscopicbase being provided by the forward motion of the aircraft. The camera is equipped with a focal plane shutter operating in a direction parallel to the flight axis. The shutter is set so that the slit traverses the film format during the time taken by the aircraft to fly a predetermined distance. I

A further feature of the invention resides in the provision of an optical method of enhancing the stereoscopic base, no lateral movement of the camera being required; This method is particularly useful when integrams are to be recorded in image formats of small dimensions, such as those associated with miniature cameras, television camera tubes, etc., as it is difficult to design and manufacture lenses which possess both large diameter and short focal length. The method involves the use of an additional optical system located in front of the camera lens. This optical system consists of a photographic lens, both the diameter and focal length of which are greater than those of the camera lens, together with an associated field lens. In effect, the relatively large aerial image formed by the first lens becomes the object insofar as the camera lens is concemed; the camera lens reimages that object to a reduced scale at its focal plane.

. It is to be understood that the scope of this invention is not restricted to the recording of images on regular photographic emulsions or on the phosphor of televisioncamera tubes; the image-recording, image-receiving or image-reproducing medium may be of any desired nature. Likewise, the invention may be applied to either still photography or motion pictures.

a In the drawings:

FIG. 1 is a diagram used in deriving the optical properties of an individual lenticule.

FIG. 2a is a front view of a piece of spherically lenticulated film, shown greatly enlarged.

FIG. 2b is a side elevation thereof.

FIG. 3 is a perspective view showing a forming tool for production of spherically curved concavities in the working surface of the die.

FIG. 4 is a similar view showing such a tool embedded in a metal rod to increase rigidity.

FIG. 5 is a view similar to FIG. 4, showing a tool having multiple forming elements.

FIG. 6a is a front elevation showing a portion of a completed die.

FIG. 6b is a side elevation thereof, partly in section and partly broken away.

FIG. 7 is a side elevation, partly in section, showing the reciprocating tool-holder in position on a typical ruling engine.

FIG. 8 is a perspective view in diagrammatic form showing a pair of cylindrically lenticulated screens crossed at right-angles.

FIG. 9a is a front elevation of a composite screen of the type shown in FIG. 8, in contact with a photographic plate.

FIG. 9b is a side elevation thereof.

FIG. is a top plan view thereof.

FIG. 10 is an enlargement of a portion of a line screen.

FIG. 11a shows a front elevation of a composite screen fonned by crossing at right-angles two line screens of the type shown in FIG. 10.

FIG. 1 lb is a side elevation of the device of FIG. 1 la.

FIG. He shows a photographic plate located behind the composite screen.

FIG. 12 is a diagram showing a portion of a spherically lenticulatedfilm'placed at the focus of a camera lens, together with a mask having twin apertures.

FIG. 13a is a diagram, partly in section, showing a portion of a spherically lenticulated film placed at the focus of a camera lens provided with a square aperture.

FIG. 13b is a diagram corresponding to FIG. 13a, the lens and aperture being viewed on axis.

FIG. is a front view of the lenticular surface, partly broken away, showing the square peripheries of the lenticules.

nos. 14a, 14b and 14 are similar, respectively, to

FIGS. 13a, 13b and 130, except that the lens aperture and the lenticules have hexagonal peripheries.

FIGS. 15a through 15f relate to characteristic features peculiar to optical imaging processes involving the use of spherically lenticulated screens or film.

FIG. 16 is a diagram illustrating the effect of the twofold image-inversion resulting from the joint action of the primary lens and the spherical lenticules.

FIG. 17 is a diagram showing lenticules with circular peripheries arranged in square array.

FIG. 18 is a diagram showing lenticules with circular peripheries arranged in honeycomb array.

FIG. 19a is a diagram showing a method of making contact prints.

FIG. 19b shows a lenticular screen laminated to the emulsion surface of the print.

FIG. 20 is a diagram showing a method of making prints, at unit magnification, in the form of transparencies.

FIG. 21 shows a modified form of aperture plate, embodying-color filters.

FIG. 22 is a diagram showing a side elevation of an arrangement for viewing a transparency both stereoscopically and in natural color.

FIG. 23 is a plan view of the arrangement shown in,

OPTICAL PROPERTIES OF THE LENTICULES.

Referring to FIG. 1, the distance i of the focal plane from the summit of a lenticule is related to the radius of curvature r by the expression:

M (1) where p. denotes the refractive index of the screen material. The value of u is usually in the region of 1.5, so, as a close approximation, we have:

l.5/i' =0.5/r

i 3r 2 The focal length f is measured from the center of curvature, and hence:

f=2r'=2i'/3 3 The maximum possible aperture is obtained when the width w of the entrance surface is that of a complete hemisphere, in the case of a spherical lenticule, or a complete semicylinder, in the case of a cylindrical lenticule. Then:

The acceptance angle 23 is determined as follows: (4) tan B w/2f B tan- (w/ 2f and The maximum possible acceptance angle is obtained when the lenticules have an aperture of f/ l .0, in which case we have:

so that 2B=2 tan 0.5000 5308 The interdependence of the various screen parameters will be apparent from the foregoing. The effects of this interdependence on the design of lenticular film suitable for use in connection with the present invention will become apparent later in the specification.

NATURE or THE LENTICULAR ARR'AY, AND METHOD or MANUFACTURE FIG. 2a depicts, greatly enlarged for the sake of clarity, a portion of spherically lenticulated film (or screenfilm combination) suitable for use in connection with the invention. In this illustration the lenticules have square peripheries and are arranged in square array. However, these are not essential requirements; the essential requirement is that there shall be no non-lenticulated areas between adjacent lenticules. (Thus, for example, it is possible to use lenticules having hexagonal peripheries, arranged in honeycomb array. This type of arrangement will be discussed later.)

Thematrix or dieused to form the lenticules may be manufactured by one or another of a number of different methods. For example, the necessary multiplicity of spherically curved concavities may be formed in the surface of a metal cylinder or flat plate by drilling. Another proposed method is to employ a machine which combines, in effect, the x and y movements of a ruling engine (such as that used in the production of line screens and half-tone screens) with a reciprocating motion in the z dimension similar to the motion of the needle in a sewing machine. Thus, the area in which the concavities are to be formed is scanned, about both x and y axes, by appropriate setting of the movements of the ruling engine. The requisite number of concave indentations is formed in that area by embossing; the embossing operation is performed by a convex-faced tool carried in a tool-holder which reciprocates in the z dimension at a frequency which is appropriately coordinated with the x and y scanning motions.

Referring to the drawings, FIG. 3 represents a single forming-tool 30 of a type suitable for production of the spherically curved concavities 31 in the working surface of the die 32 shown in FIGS. 6A and 6B. FIG. 4 shows a forming-tool 33 of the same type embedded in a metal rod 34 of larger diameter in order to increase its rigidity and facilitate mounting of the tool in the tool-holder of the embossing machine. FIG. 5 shows a cluster 35 of forming-tools of the type shown in FIGS. I3 and 4, the object of this arrangement being to reduce the number of strokes that must be made by the embossing machine in producing a die of given size. FIGS. 6a and 6b represent a portion of the completed die 32. The die illustrated is assumed to be made of a material, such as a thermosetting plastic, which is capable of being softened slightly by the heating effect of an electrical current in circuit 36 in order to minimize tool wear during the embossing operation. After completion of the embossing operation, the die 32 is permitted to cool and reharden, and then mounted on a metal backing plate 37 to increase its rigidity. The backing plate may be curved (e. g., cylindrical) or flat, depending upon the type of process to be employed in manufacturing the lenticular film or screen. After mounting of the die 32 on the backing plate, the working surface is metallized (e. g., by electrodeposition) as shown at 38 in order to increase its hardness. FIG. 7 shows a portion of a typical ruling engine 39 adapted to perform the embossing operation, and having the forrningtool 33 mounted in the tool-holder 40 and acting on the die 32. This particular ruling engine 39 is disclosed in US. Pat. No. 2,575,367, but this is by way of illustration only.

As previously indicated, it is possible to simulate the effect of an array of spherical lenticules with square peripheries by the use of a pair of cylindrically lenticulated screens 41 and 42 (FIG. 8), crossed at right-angles. In FIGS. 9a, 9b and 9c this composite screen 43 is shown placed in Contact with the sensitive surface 44 of a photographic plate 45 or other suitable photorecording medium to produce the photographic equivalent of the arrangement shown in FIG. 2a. A further optically equivalent arrangement is obtainable by the use of a pair of line screens 46, having a relatively high opaque/transparent ratio, of the type shown, again greatly enlarged, in FIG. 10. A pair of such screens, when crossed at right-angles, results in a composite screen 47 having a multiplicity of minute square apertures or pinholes as represented at 48 in FIG. 11a. In FIG. 11b, the composite screen 47 is shown, in side elevation, located in front of a photographic plate 49, FIG. l1c. Although this arrangement is basically similar to that represented in FIGS. 2a and 2b, it is to be realized that (a) the arrangement shown in these earlier diagrams is inevitably faster in the photographic sense due to the fact that the f-number of the lenticules is smaller than that of the square apertures, and (b) the resolution of the arrangement in FIGS. 11a to 11 is inevitably much lower due to the fact that a substantial portion of the imagery transmitted by camera lens is obstructed by the opaque areas between the apertures.

FUNDAMENTAL CONCEPTS Referring to FIG. 12, this diagram is intended for use in explanation of certain optical characteristics of the invention, although the actual combination of elements illustrated does not represent a feature of the invention. The diagram shows a piece of spherically lenticulated film F placed at the focus of a camera lens 0. The lens is assumed to have a large effective diameter, preferably greater than the normal interocular distance of about 2% inches. An opaque mask M is located close to the lens, this mask being pierced with a pair of small, laterally spaced circular apertures, L and R, the separation between the apertures being approximately equal to the normal interocular distance. As a result of this arrangement, the small portions of the lens which receive light entering through the two apertures function similarly to two separate lenses. Thus, a left-eye view of the subject is directed toward the fihn by one element and a right-eye view is so directed by the other element. The lenticules on the film reimage these two views as a large number of minute, disc-shaped images. Each such disc, occupying but a fraction of the area of emulsion behind the associated lenticule, contains a minute image of some small element of the subject. The left-eye and right-eye images are interdigitated laterally across the film emulsion as denoted in the diagram by, respectively, I and r.

Consider the mask M to be pierced with a third small aperture located midway between the apertures L and R. This will result in the formation of a third array of little disc images, interdigitated between those denoted by l and r. It will be clear that the third view constituted by this additional array of images will represent an aspect of the subject which is rightward with respect to that due to the aperture L, and leftward with respect to that due to the aperture R.

Next, consider the mask M to be pierced with further small apertures at intervals extending, not only across result in the formation of a further array of image elements displaced from their neighbors byamounts, and in directions, dependent upon the location of the aperture in the mask M.

Now consider, finally, that the mask M is entirely removed, this being equivalent to introducing a sumciently large number of overlapping apertures. The image formed behind each lenticule will now be a small disc-shaped image of an element of the subject, the aspect of that element which is presented by the disc image changing progressively along every axis in the plane of the disc. According to the values chosen for the optical components of the system, matters can be so adjusted that the little'disc images are either spaced apart, just abutting, or overlapping; under any of these conditions, moire effects will be exhibited by the completed picture. In order that such moire effects may be avoided, or at least reduced to a level at which they are not obtrusive, it is necessary to arrange matters so that adjacent elementary images in the array of which the picture is composed are precisely abutting, and not appreciably overlapping or spaced apart; moreover, it is desirable that the entire area of the photosensitive surface within the film format shall undergo exposure, but not multiple exposure. It will be evident that it is impossible for all these conditions to be fulfilled if the elementary images are disc-shaped. Thus, for example, with disc-shaped images, matters can be so adjusted that each disc just contacts the periphery of each of the adjacent discs. However, such contact is possible at only certain points on the periphery of each disc, thus leaving a multiplicity of unexposed areas.

It is a feature of the present invention to provide means for modifying the shape of the elementary images so that the conditions necessary for obviation or minimization or moire effects can be achieved. One of the preferred methods involves the use of a plate or diaphragm having a square aperture as shown schematically in FIGS. 13a and 13b. The effect of this aperture plate, used in conjunction with lenticules having square peripheries, is to change the shape of the elementary images from circular to square, and to provide that the sides of adjacent squares are precisely abutting, and neither overlapping nor spaced apart. It is possible, at least in theory, to fulfill the required conditions by the use of elementary images having a shape other than square or hexagonal, but departure from the preferred shapes introduces problems in the manufacture of the lenticular screen and in other areas without yielding any additional advantage to offset these difficulties.

FIGS. 14a, 14b and 14c are diagrams similar to FIGS. 13a, 13b and 13c, respectively, but the aperture and lenticules have hexagonal peripheries. Both sets of diagrams will be considered in more detail later.

IMAGE ORIENTATION a regular camera lens, the orientation of the numerals, as viewed from the back of the camera, will be as indicated in FIG. 15!). If the image is recorded on a photographic plate or film, a print can, of course, be made; this print, after rotation through 180 in the image plane, will display the numerals in the same orientation as that of the numerals on the target. The print is represented by FIG. 15c, which diagram is identical to FIG. 15a.

Now consider FIGS. 15d to 15f, the target being represented by FIG. 15d. The remaining two diagrams illustrate the results of imaging the target bythe method described below. Consider four adjacent spherical lenticules, in square array, on a piece of film or a screen used in conjunction with an imaging system of the type shown in FIGS. 13a and 13b. The image formed at the focal plane of an individual lenticule is not an image of the entire scene within the field of the primary (camera) lens; it is an image of some minute portion of that scene, which particular portion being dependent upon the location of the lenticule within the camera format. Accordingly, it is to be assumed in the present case that FIG. 15d represents just a very small portion of a much larger target, the portion illustrated being of such dimensions that its image precisely fills the area of the total format of the four-lenticule array. Now, in the absence of the lenticules, the image would be oriented as shown in FIG. 15b. However, due to the presence of the lenticules, the elementary image within the format of each individual lenticule undergoes rotation about its center through 180; accordingly, the orientation becomes as shown in FIG. le.

In order that the complete picture (of which FIG. e, as previously indicated, represents just a small part), in the form of either the original or a print may be viewed the right way up, it is necessary. for the complete picture to be rotated through 180. This further rotation results, finally, in the orientation represented inFIG. 15f. Thus, the picture as a whole is now the right way up, element No. 1 being above element No. 3 and to the left of element No. 2, while element No. 4 is below element No. 2. However, each individual element is now inverted; in consequence of this inversion, the panoramic effects exhibited by pietures produced by this technique are the opposite of those experienced when viewing an actual threedimensional subject or scene. Thus, when viewing an actual scene, if the observer moves his head to the left, a more leftward aspect of the scene is presented to his eyes; if he moves his head to the right, then the view presented to his eyes is more rightward in aspect. Again, when viewing a real-life scene, if the observer raises his head, the aspect of the scene presented to his eyes changes to one appropriate to his more elevated viewpoint. Similarly, if .he lowers his head, the aspect changes to one appropriate to his lower viewpoint. However, in the case of a picture produced by the method under discussion, the changes in aspect which result from changes in the observers viewpoint are the opposite of those just indicated. If, for example, the observer moves his head in a lateral direction, then the aspect of the image presented to his eyes becomes more rightward if he moves his head to the left, or more leftward if he moves his head to the right. Similarly, if the observer moves his head in a vertical direction, the

aspect changes to one appropriate to a lower viewpoint if he raises his head, or to one appropriate to a higher viewpoint if he lowers his head.

It is found, in practice, that the anomalous effects referred to above are not at all disconcerting to the observer; in fact, they will usually pass completely unnoticed by him unless his attention is drawn to them by someone who is familiar with the optical characteristics of the process. There are, moreover, methods-generally involving sequential printing or reproduction-by which these anomalies can be avoided so that the panoramic effects are consistent with those observed in everyday visual experience. These methods involve rotation of the individual picture elements, instead of the array as a whole, through 180 in the image plane. There are potential uses for such procedures in some electronic (e.g., television) applications of the invention. For example, inversion of the picture elements displayed on, say, the screen of a cathode ray tube can be accomplished by appropriate design and arrangement of the scanning circuitry.

It might, perhaps, be thought that inversion of the individual image elements, as represented in FIG. 15f, would result in impairment of the quality of the picture. However, in general, such is not the case for the following reason. In most practical cases the image elements are so small that the information within the area of a single element is insufficient for identification as a feature of the picture. Such identification is made possible, however, by the eyes ability to recognize the larger amount of information contained within the net area of several adjacent elements. As an analogy, consider the case of a lithographed color picture which, as is known, is composed of a large number of groups of minute colored dots; unless a very coarse screen has been used for the lithography, neither a single dot nor even a single group of dots can be discerned by the naked eye, and several adjacent groups of dots are needed to construct an identifiable detail of the picture. It is, moreover, a demonstratable fact that each and every group of dots can be rotated through .180" (or any.

other angle) about its own center without producing any observable effect on the picture. Such rotation through is, as will be understood, equivalent to image inversion of the type discussed in connection with FIG. 15f.

FIG. 16 illustrates, in a simplified manner, the effect of the twofold image-inversion resulting from the joint action of the primary lens and the spherical lenticules; that is to say, the diagram shows why a contact print, a reversal positive or a negative produced in accordance with the invention may be seen either stereoscopically or pseudoscopically, depending upon the observers viewing distance. The sketch represents a piece of spherically lenticulated film being viewed by an observer, first from position (a), and then from the more distant position (b). In each instance the observers left and right eyes, respectively, are denoted by E and E At the focal plane of each lenticule, the numerals l and 2 are used to denote the edges of the elementary image depicting, respectively, the extreme leftward and extreme rightward aspects of that image. Thus, for the picture to be seen in the stereoscopic mode, light rays emanating from points in the elementary images nearer to the edges denoted by the numeral 1 should reach the 

1. A stereoscopic photographic system comprising: a primary lens originally having a circular aperture of radius r; an aperture plate located in the plane of one of the lens pupils having an aperture therein with a square or hexagonal peripheral configuration and having a half width s between opposite parallel edges, where s is equal to or less than r/1.4142; a combination multi-element screen and photographic backing means positioned a distance i from said aperture plate, said combination being located substantially at the focus of said lens, the elements of said screen having a square or hexagonal peripheral configuration matching that of the aperture in said aperture plate but on a reduced scale with respect thereto and each element having an acceptance angle of 2 tan 1 s/i, the characteristics of the lens, the aperture and the elements being so coordinated that the elementary image at the focus of each element on the surface of said photographic backing means substantially fills the image format of that element so that adjacent elementary images are neither appreciably spaced apart nor overlapping.
 2. The stereoscopic photographic system defined in claim 1, in which said screen comprises a lenticular screen having square or hexagonal lenticules shaped and oriented in a space-filling configuration so that there are no appreciable non-lenticulated areas between adjacent lenticules.
 3. The system claimed in claim 2, wherein the surfaces of said lenticules have substantially spherical curvature.
 4. The system as claimed in claim 1, wherein said multi-element screen comprises a pair of cylindrically lenticulated screens extending at right-angles to one another with the lenticulated surfaces thereof in contact with one another.
 5. The system defined in claim 1, in which said multi-element screen comprises a member of opaque material having apertures therein of the same configuration as the aperture in said aperture plate but on a reduced scale with respect thereto.
 6. The system as claimed in claim 2, wherein said combination is a composite unit, said light-sensitive backing means being a photographic film comprising a transparent base, one surface of which carries light-sensItive emulsion, said lenticules being formed on the surface of the film base opposite that surface which carries the light-sensitive emulsion.
 7. The system as claimed in claim 2, wherein said combination comprises a photographic member and a separate lenticular screen adjacent said member.
 8. The system as claimed in claim 1, in which said aperture plate is located in the plane normally occupied by an iris diaphragm.
 9. The system as claimed in claim 2, wherein the lenticules of said lenticular screen are defined by square peripheries, and said aperture in said aperture plate has a square periphery.
 10. The system as claimed in claim 2, wherein the lenticules of said lenticular screen are defined by hexagonal peripheries, and said aperture in said aperture plate has a hexagonal periphery.
 11. The system as claimed in claim 1, wherein said aperture plate includes color filters so that the area of the imagery occupying the format of each lenticule is subdivided into smaller areas corresponding in respect of number and shape to the filters in the aperture plate, thereby causing the gray scale of the associated portions of the imagery formed on the light-sensitive backing means to be modulated according to the amount of light transmitted by the corresponding filters in the aperture plate.
 12. The system defined in claim 11, in which the photographic backing means comprises a black-and-white transparency, and which includes a light source positioned to direct light through said lens and color filters to said transparent combination, and which includes a multi-element screen positioned between an observer and the aforesaid transparent combination.
 13. The system as claimed in claim 1, wherein the size of the aperture in said aperture plate is adjustable. 